With increasing popularity of mobile voice and data communication, there is an ever increasing demand for high-speed data communication. The Long Term Evolution (LTE) communication standard was developed to accommodate increasing capacity and speed for data transmission over an air interface. LTE is standardized by the Third Generation Partnership Project (3GPP), with Release 11 being the most recent Release of the LTE specifications. The air interface of LTE, called Evolved Universal Terrestrial Radio Access (E-UTRA), is based on and represents an evolution of wideband code division multiple access (WCDMA). The WCDMA specifications are also promulgated by 3GPP.
In addition to high speed and high capacity, long battery lifetime is an important factor for users of a user equipment (UE). Discontinuous reception (DRX) is one technique which may be user to reduce an average power consumption and thereby increase battery lifetime. In a DRX state, the mobile terminal or other UE is allowed to power down for certain time periods and the network knows not to send transmissions to that mobile terminal during these time periods.
In LTE, according to 3GPP E-UTRA specifications, a terminal can be in different modes (also referred to as states). The modes include an idle mode which has the lowest power consumption. The modes include a connected mode, which may have several sub-states. In the various sub-states of the connected mode, the UE may be in a Radio Resource Control (RRC) connected state. The sub-states may include at least one sub-state in which no DRX is performed, and one or several sub-states in which DRX is performed. The purpose of the different modes is to define a good balance between required network resources, UE power consumption, and data traffic delays.
When the UE initiates a new data transfer it will move from idle mode to an active state and will stay in the active state until no data should be immediately transmitted. At that point of time the UE will be moved to a DRX state. After an inactivity timer timeout, the network will cause the UE to make a transition from the connected mode to idle mode again.
The inactivity timer which determines when the UE will be caused to make a transition from the connected mode to the idle mode is also referred to as “inactivity timer T3” in the art. The inactivity timer value which determines the time period after which the UE will be caused to make the transition to idle mode again defines the time period for inactivity over the air interface after which a radio access network (RAN) sends a message to the UE to move it to the idle state. This inactivity timer value is typically not transmitted to the UE. The inactivity timer T3 is maintained in the RAN, and a node of the RAN transmits a message to the UE to indicate that the UE shall enter the idle mode.
The inactivity timers which determine when the UE shall make a transition to a mode with lower energy consumption may be configured by the RAN according to a suitable decision algorithm. The decision algorithm may take UE power consumption into account. However, it may still be difficult for the network to set proper inactivity timer values, since the parameters which are set are compromises between different aspects which include data traffic delay, UE power consumption, and network load, as well as possibly other target quantities.
With a view to battery lifetime of the UE, it would in general be desirable to only be in the connected mode without DRX when data transmissions are ongoing, and then move into the state with lowest power consumption very quickly, which typically corresponds to the idle mode. This could be achieved with short inactivity timers. However other aspects are considered in the network. For illustration, the amount of signalling required to cause a UE to change between modes or sub-states as well as the additional delay before data transmissions that could be a result of frequent changes may cause the RAN to keep UEs in active states for many seconds after each data transmission. This may be inefficient as regards the battery lifetime of the UE.
There are various scenarios in which the inactivity timer value which governs transitions from the connected mode to the idle mode set by the RAN causes too high power consumption in the UE. On exemplary scenario is when the UE has to perform an RRC reconnection which occurs with a short delay after the UE has been moved to idle mode.